Booster for hydraulic control system



June 14, 1960 G. E. PORTER 2,940,261

BOOSTER FOR HYORAULI'C CONTROL SYSTEM Filed June 2e, 1959 nited States Patent BOOSTER FOR HYDRAULIC CONTROL SYSTEM Gilbert E. Porter, Escondido, Calif., assigner-.of one-half to Gunter Krause, Los Angeles, Calif.

Filed June 26, 1959, Ser. No. 823,093

The present invention relates generally to hydraulic control systems, and more particularly to a booster which can be placed in an hydraulic control system for the purpose of increasing the ultimate liuid pressure dethat of maintaining a maximum braking force over an appreciable length of time. Usually it is necessary to have :the assistance of some type of power unit which is designed to apply a part or all of the operating force, a vacuum power unit being in this category. The initial thrust upon the foot pedal can be quite vigorous and is ordinarily adequate to give a rm application of the brakes even without any power or assister unit. Because of the momentum of the parts, and because it is possible for the driver to exert a relatively strong thrust for a short time, a high uid pressure can be initially built up in the brake system. During this initial period, the maximum output for applying the brakes is developed. However, if it is desired to maintain this maximum braking eliort for a long time, the driver of the automobile may encounter considerable diniculty in doing so because of l muscular fatigue. This is especially true in the case of elderly people or others whose leg muscles 'are not particularly strong or well developed. The weight of modern day automobiles and the high average speed at which they are operated, combine to create a correspondi ing high demand in the work which the brakes are called upon to do in stopping a vehicle. This is particularly true in the case of commercial vehicles; Ybut it is also true in passenger automobiles wherein the brakes are applied by a force exerted on the brake shoes through an hydraulic control system.

These conditions presentin modern automobiles have' brought about the need for larger and heavierbrake systems. This has been accompanied by a corresponding increase in the operating pressures required in vthe hydraulic system, which in turn require a greater exertion by the operator lto achieve and maintain a maximum thrust on the brake pedal for an extended interval of time. AIf maximum pressure in the hydraulic control system can be attained more easily and maintained with less physical exertion than is required in known .types of systems, a greater .margin of safety is-afforded the driver; This condition is of a special benefit Ato drivers who, because of their size or physical condition, are unvalves are mounted on moving parts and consequently lthere must be a certain amount of movement in the deable to operate vehicle brakes as vigorously and as` rmly 2 vice before it becomes operative. This developes a slack period in the operation referred lto as loss of pedal is disconcerting to the driver and may impair optimum performance of the unit. In other designs, the devices develop a jerky action in shifting from one mechanical advantage to another. This is very annoying to the driver.

Thus it becomes a general object of my invention to provide an improved design for a hydraulic booster unit which may be incorporated in conventional hydraulic control systems for vehicle'brakes and the like in order to provide for easier establishment of high fluid pressures in the system.

Another object of the present invention is to provide a unit for increasing hydraulic pressure within a brake system over that provided by the usual master cylinder and which has a of moving parts to insure reliable operation and long life.

A' further object is to provide a booster unit of the character described which is smooth in operation over the full range of movement and gives .the driver -a sure, iinn control of the vehicle at all times.

Another object is to provide a booster of the character described 'which may be built as a self-contained unit that may be sold as an accessory and can be easily modified lto permit adding it to any one of many existing brake systems on passenger vehicles of current design, without lexcessive costs and without any interference with the proper operation of .the brake system.

These and other objects have been attained in a booster unit of novel construction embodying my invention and consisting of a housing having an internal bore forming a differential cylinder. A`stationary stem extends axially through the housing and defines an axially extending uid passageadapted for connection at the inlet end to a source of uid under pressure, which is ordinarily the master cylinder. of the brake system, and -for connection at .the other end to theY cylinders operating the brake shoes. A differential piston having end faces. of dile'r.- ent effective areas movable axially within saidv cylinder is located within the housing and is likewise movable Ywith respect Vto the stem. .A check valve is located in the uid passage in the stem permitting ow through the passage and past the valve only Kfrom the inlet'end l.to the :outlet'endf Springmeans urges the piston toward the larger endof the cylinder'in which positionthe various ports in the hollowstem communicating with the interior of the cylindefrare all uncovered. A rst port in the stem places vthe interior of the stem in communica- :tion with the space within the cylinder at one end of the piston while a second port places the stemrinterior in ing bolt by lwhich `the booster is attached directly to the master cy'flinder.v I

How the above and other objects and advantages of my invention, as lwell^-as"others 'not specifically mentioned herein vare attained will be more readily understood by referenceto the -following description, and to the annexed drawing, in which:

Y i lisa longitudinal medianl section through a brake boostery constructed according to my invention, the parts being shown Vin the rest position occupied when the brakes are released. i;

,.lig. 2 is a view ,lsimilar-to Fig.:1 but showing, positions of parts during application of the brakes and after 3 the piston has'tbeen movedzto the left from the rest position to. cover one of the V`ports ,in Y,thestetn Fig. 3 is a fragmentary `medi-an section showing the valveY open at the beginningfof application of the brakes. iiRefrringnowtolFig. l; titte1 b oostertas embodied iin a preferred form of my yinventiorn'is generallyindicated at Bi Inthis form nfthefinzentiontit isshovvn as an accessory iunit which cangbe addedV tothe m'aster cylinder, indicated generally :atnC,` that isjmo'unted'onfthe` vehicle andpovides'asource of fluid under pressure; Themaster cylinder andY its.Huidireservoirgmaydzeof any l:known de signr suitable-"for y this pirpos'eiand rconsequently the fria'sfer: Vcylinder isfshown onlyfragmenta'rilysincejts2 tionstrrctio'ii fpnns ire'jpan;eithefpresentfivention:z fifi# *Booster-iB Ycomprisesa; neiisglo finadezinfitwo parts Inland 12 which are'conneeted centrally otheidiou'sing any suitable mnner',V asfpytfafserew-threade Eajelrfof the housin'gis'eetions is`^ niernlqer having ai' cylindrical b" 'hou'si'ngsec'tioi Iltis s'ndallerin housing section 12 so that-'whenl" ianteter' than hiffinsde snafus'aanneemtwhen@1enieuwe has sealing; members l 17 j and V18 at the gerandi smaller nsasiffeivrall t A4 hollow ste rid 5to the other: Berthe s dranlicfiuid atrthesenpoints. n ,Y

:rapinata 15 vwhich, has

onlynthestem 4needbe made special yforreata differentl in-V stallation. '11n this arrangement Ythe stem serves Aas 4a'nboltior mounting the Ybooster on'the mastervr cylinder. Y

One endfuidtpassage Z6 is open/to the interior of the masterrcylinderwlicli supplies lgiydiaulie uid under pressure to'theLhooster. other end of the stem is internally threaded at Z for connection to the hydraulic lines of the brake system and is accordingly termed the outlet end. V'l'li'ese'hydraulic lines are indicteddiagramrnatically atm29 andconductthe hydraulic under pressure to the individual wheel cylinders 3i) whichtareguid motorstfor moving the brake slices into V-engarge'mentvvith'thebrake drums ofthe vehicle. VInits broader raspectsyof coursertliebooster of the present invntion umay-be jconncctedL to anyv other type of luid motormeans.' Y 1 :ocatediwithin iiu'idV passage 26 intermediate'` the ends of"stem.25 isa check-valve'whichfis arranfrcdto permit uid ow forithe full length oftlie-passa'geandpast the valveronlyzfromthe inlet endnat` the master cylinder towardthe 'outlet end VforV discharge to conduit 29. This checlrvalve` may? be of anysuitable coijlstrttction` but is `lierre' 'shown'asconsistingoflball valve 3 1 which ispressed byfspring A33 into engagement 'with an annular fseatz IVfcrined'iby a shoulder the passage: Spring bears 'at one endiagainst a snap i'ing-'i` held in a groove in the enlarged?v portion `of passageway; 26 and bears'v .at the otherv end' against. ball 31,*the compressionV in V'the spring 'normally keeping the ballseatedY against valve seat-:32. Hovvever'spring 373 ryields to fluid pressure applied through passageway 26 tothey inlet side ofthe,check:val`ve. The duid-pressure moves therballlcheckaway from the seat tofop'enthe valve as seenin Fig." 3 and permit hydraulic luid? to iioyvjpast the Valve `toward the outletv end of stem l1 'stem -zs ts provieedrwith thrpmrswhich afford r'connn'unication between fluid passage 26 within"thestem and the *cylinder-'sfaces` 11s andy 12s withinY the housing btfoutside'offstem '25. yTlie's'efport's nijaybe'inl each case single openingl in'thesteniwall; bt-re-preferably f dejas ia: plurality vc4 feopfei1i11-'gsfsY shfiywn in'the jdr'aw'- n. l rd' Y providegsucientfarea Ya'teacli 4port'for trans er :offliyclrauliciluidjthroughv the p'oitsy Start- Aing at,therinletend "ofjtllerboosfer, '-thelii'stY 'porti' isf-in# f 'dicatedat 36h 'andjisi located pnjthestem vat su'chga positionftla'atA if opens to the i exterior off thek rsteinr''in'` tl'ie9`recess 22 cut inrfthe endwfacrepof itliejditferenti'al'pist'on. #Itiniltbegtwticed 'fram .Fier-14" thatwhmthffdirfal Pisten. visi @fthe extreme, of itsY mevementttletrisht, fa l* viewedjn that figur-@1 andjin Yengagementwith 'the end `the piston, V'that port 36V not covered-by the Also,- recess 122 e is in 'cornrnnnicationY through ston' vvhen inthe 'normal or 'rest'positionl In the interior 26 of the stem and the cylinder space 11s Within the housing and around the stem at the smaller end of the differential piston.

Housing 10 is provided with one or more bleeder plugs 40 and 41 which close openings communicating respetaI tively with the cylinder spaces 11s and 12s at the smaller and larger faces of the diterential piston. These aredesigned to allow air to be bled out of the housing after the system is filled with hydraulic nid. For this reason the openings for these bleeder plugs are located at the top of the housing when installed. Proper positioning of the bleeder ports is simplified by the fact that the vhousing is stationary while the sten is being turned to mount the booster in place. After all air is removed from the system, plugs 40 andv 41 are inserted in threaded openings.

The space 43 between the smaller diameter of the piston and the larger diameter cylinder bore in housing section 12 has no air bleed and may contain some trapped air, or it may operate under a partial vacuum. Air that escapes from this space can be bled olf at 40 or 41.' Lack of an air bleed to the space 43 is no disadvantage in operation and prevents access of air to the system that eventually can produce a spongy action of the piston.

Having described the construction of a preferred form of my invention, I shall now describebriey its operation. It will be understood that, when the brakespare' applied, uid passage 26 and the two chambers 11s and 12s are already completely filled with vtluid. When the yehicle'operator applies the brakes, as by depressing the familiar foot pedal, the master cylinder is caused to 'deliver hydraulic uid under pressure, as is well known in lat) theart. This iiuid under pressure leaves the master cylinder C .and enters the booster through the inlet end-of uid passage 26. Spring 33 is a relatively lightspring so that only a small excess of pressure on the inlet side of valve 31, causes itj to open as Ain Fig. 3, allowing the uid to ow through passage 26 and out of the outlet end thereof to hydraulic lines 29 which conduct the duid under pressure to the motor means 30. Since port 37 is relatively small, the resistance to tluid llow out through port 37 into space 11s and then back into the stem through port 38 is sufficient to cause the hydraulic pressure to open check valve 31. Pressure in the fluid is communicated to both chambers 11s and 12s at opposite sides of the dilerential piston through ports 37 and 36 respectively.

Valve 31 opens instantly that uid begins to move through the booster. The valve being fixed in position and not on a movable member reacts to fluid ow immediately. The result is no spongy action or loss of pedal as occurs when an appreciable volume of uid must flow prior to opening the valve.

The initial period of applying the brakes is referred to as the preloading period. During this initial period the brake shoes are expanded into contact with the brake drums, but little if any actual braking force is applied to the shoes. Most of the movement Within the system occurs as action preliminary to' actual braking. During the preloading period, the uid pressure in both chambers 11s and 12s increases because they are in free communication with iluid passage 26. Since these two chambers are already lled, there is yet no ow of fluid through ports 36, 37 and 3S and all of the uid entering passage 26 from the master cylinder ows through it past valve 31 and into hydraulic lines 29.

At some point in the application of the brakes as determined by the strength of spring 20, the preloading period terminates and the compounding action of the booster commences; and it is the commencement of the compounding action that is designed to coincide as closely as possible with the actual brake application. This transition from the preloading period to compounding action takes place at somev predetermined Huid pressure inthe system, -u'sually somewhere .in the'range of 12S-i 200 p.s.i. changeover takes place .when the uid pressure in cylinder space 12s 'and recess 22 exerts va force against the effective varea at the largerendof the differential piston which exceeds the opposing force applied to the smaller end of the diierential piston. .This opposingforce is the sum of the forces exerted on the effective area. at the smaller end of the dilerential piston produced by the hydraulic fluid in the smallerchamber 11s`and the force exerted by spring.20. When the total force to the left (inFig. 1) on the piston produced by hydraulic uid in the large diameter space 12s exceeds .the sum total of the two opposing forces, differential piston 15 ,moves forwardly to the left from the position of Fig-'l to some-position such as is shown in Fig.2. v;

The pressure is communicated from passage 26 through port 36 tothe uid in recess 20. From here the pressure is communicated through slots 21s to the uid in space 12s, extension 21 lbeing in contact with the end wall of the housing. Hence the net area of the annular extension in such contactis not exposed to iluid pressure. When the piston has advanced out of contact, this annular area is lexposed to uid pressure, being then a part of the net effective area exposed to fluid pressure at the larger end of the piston. The small size of slots 21s ,and the area of annulus 21 are designed to slow up the initial -build up of fluid pressure in space 12s around the extension and to make the changeover to compounding action less abrupt than is otherwise the case. The result is ya smooth braking -aotion in which the driver does not feel .the change to compounding action.

When the piston has moved forwardly for a short distance, it covers and closes port 37 and hydraulic uid4 in cylinderspace 11s is trapped ahead of the piston. Such fluid is then forced out of thercylinder space and into the hollow stem through port 38 by continued movement of the piston. This producesau increase in pressureon the outlet side'of valve 31 to cause the valve to seat, returning the valve lfrom the open position of Fig. 3 to the closed position of Fig. 2. With the check valve closed, iuid in the cylinder ahead of the piston ows out of the cylinder space 11s and into hydraulic lines 29 to actuate the vehicle brakes. However, it will `be understood' that there is ordinarily little actual displacement of uid during this compounding period since the brake shoes are already in contact with the brake drums and consequently the principal eiect during this part of the brake applying period is only to increase the hydraulic pressure-in the system in order to exert the desired force by the brake shoes against the drum. This is accomplished by increasing the pressure from the master cylinder and the action of the assister unit. Fluid owing out of the master cylinder enters the assister at the inlet end of passage 26 and then flows through port 36 into cylinder space 12s, advancing the piston. A

The force exerted by this iuid on the dilerential piston in a -forward direction, that is toward the left in Fig. 1, is equal to the unit pressure of the hydraulic iluid multiplied by the elective area of the piston vface at the inlet or l-arge end of the piston. As long as this total force is greater than the opposing force it moves the piston to the left. As a result, the unit uid pressure in the cylinderspace 11s at the outlet end of the piston is increased overthe unit pressure at the inlet end in the inverse ratio of the elective areas at the two ends of the dilerential piston, neglecting the eiect of spring Z. The increase in the output unit pressure relative to the inlet pressure is the Iresult of the so-called compounding action of the unit.

When the brakes are released, the Huid ow is the reverse of that described as it returns to the master cylinder C. The pressure in the hydraulic lines and the force drives it to ibex. position oaf Eig. 1. .inl which eextensionl 1 onV i the :pistoniengageshuadjacentgenxkmmllnof, housing loto-limit the `vpistonftx'avel. .lhepis'toniis'stoppd short depthofrecess ZZ-arelnideisuchireltivegtithe luc'a'tion of port 36 that port 36 cannot be covered by the .isti

Yvarious changes iin Vthe 'design vanddetai1e'd arrangement ofl thelc'omponentpartssof-my .loo'steriunit VVmay;'fceunto persons skilled in the artbutwithoutndeparting'frmithe spirit andscope ofi-myinvention.` -Accordinglyfitis'to be understood-that theforegoing-descriptioniis considered as being Lillustrative mi?, -rther v'than limtatiyempon, the invention as -dened -by 4the lappended fclaims Y l Y l. Inl a fluidi. pressure Abooster "for A-anhydrz'ulio :coh-

trol system, the'combinatomcomprising: Y

thrzugh the "stemtvonly 4from sid inlet tosaidy outlet end; an i, \Y,",.l. i Fs'lzuil'g mes urinthe1iston towrdfthe larger end Volf: tHe ylinrjsaid stern havingarst port-11i l-aV second port placingthe cylinder spaces nt the larger -andgsfnyialler' end, fce's respeetivel-y`of.` the `piston infornmuniction with thefuidpssage inside of the stemjat oppositesides ofthecheckvalve.fV 1 f f n Y VVA2. A'uid pressure hoostersiclaimed in clim 1 which also includes ineens gflorlper'mitting return Viow of hyf druliciiuid round the check value when the check Valve isclose.Y y f- 3,. Aiuicl pressure :boostergasclixned in k elaine 2 `that alsesnlusdsxga thirimort. ingfhe, Sie@ ,'Prevdin. 5111i@ cornmunieationf-fbetween the axially extending ,passage md thefylinder:spatthe Smaller A"and12eme-:evi me. his: ton, vsaid* third po'rt being Withinthelrangeof `trgyelof, the piston toghe;.:oyeredthereby while operating pressure is -beingeppledto theiluid. A

.4. Afuid5pressu1e jhoosteras claimed inmlaim'l .that als@ illludes. vstop means t 1i1.11itY trai/'e1 of; the Ynistorn under theurging of said rspring to prevent -thepiston from coveringthe` :ilstportL ,i

.5. ,A` iluidpressuregbooster as claimedin claim4 in whichvihe Stop means is an annular extension of the pistonengageable'.Withnanend wall of the housing.

y6`.A,iluidrpressure hoosterasrclaimed'in clainiil ,in whichlhe. seat of the `check valve yis stationary lrelative to the,housing. s i Y l A s ;7 ;A Vfluidsl ,pressure booster ias Vclaiimedpin Yelaine lfiu which fthegstemi is rotatable with respect 'tothe` housing and-is provided. with means yfor mounting the boostl-on the lsoureA of uicl.l under pressure.

`8. A uid pressure booster -as cliihd in'clainl lfi ywhiclinll thefnternl spees lof the booster tre isolated :freni tkeatmosfmere No references' cited. 

